This invention relates to a method and apparatus to implement a video bus network using standard video components (videotape recorders and cameras).
Video surveillance systems are mostly used in banking applications. Their use, however, may extend to government sites and several other locations where security is an important issue.
Traditional video systems are illustrated on FIG. 1. This type of system comprises a scanning device 22, a monitor 20, a videotape recorder 20 and several cameras 24. Each camera has a dedicated connection to the scanning device. The scanning device selects an image from a camera, displays it for a few seconds, records it in the videotape, and then switches to the next camera. If the system operator detects an unusual event on video, he may switch to the camera that recorded that event and follow the suspect until either a criminal act is committed or the suspect leaves the protected area. All these events are recorded on videotape so that security officers may search the videotape for events in the past.
This design, however, has several drawbacks. For instance, the recording system only stores the current image on display. In a large system comprising several cameras, it may take a long time for the system to return to any one camera. Thus, a person can take advantage of this and commit a criminal act without being recorded by the video system.
Another drawback of this system is its physical connection. Each camera has a dedicated link to the main scanning system. Thus, a large system requires an equally large number of dedicated connections. As the system grows, the connection setup will become harder.
A partial solution to this problem has been proposed in the past (U.S. Pat. No. 6,104,428), by means of a system comprising a single video bus, several camera systems and a special monitor-control unit (FIG. 2). The camera systems (FIG. 4) comprise a microcontroller 44 and a video switch 42. The microcontroller adds addressing capabilities to the camera and manages the video switch. Hence, only the camera system with a correct address may transmit video. The control unit manages the address and selects the active camera.
This system transmits control signals using a vertical retrace signal. The control signal is modulated an embedded on the vertical retrace section of the video signal. Using this, only one link is used to connect several cameras and the control unit. The control unit encodes the control signals, and must have video recording capabilities. This is a significant drawback, since the recording unit must be able to encode the control signal, making it difficult to set up using standard components.
In addition, the camera system has a demodulator embedded on the video switch 42, increasing its complexity. The full system cannot work using standard components, limiting this system to a brand name. This limitation results in a system incompatible with industry standards.
The use of a unique link for both control and video signals has a major drawback: if the connection between a device and the main system is lost, both video and control signals will be lost, and the system will not be able to automatically detect the failure.
A video bus system must be flexible and independent from its components. Such design requires the addition of external components to control the video signals. The use of external components does not degrade the quality of the video signal and adds more features to the complete video system.
The target of this design is to have an independent control system. Using dedicated master and slave devices, the video bus system remains independent of manufacturers. Finally, using separate video and control signals provides the ability to detect failures in slave devices.
The main object of the present system is to implement multi-channel video recording using a single video bus and standard video components.
Accordingly, several objects of this system are:
a)Easy setup: The use of a single video bus makes it easier to set up the system. All cameras use the same link, so adding new cameras is very simple;
b)Compatibility: The use of standard video components makes for a more flexible system. Cameras may come from different manufacturers;
c)Image storage flexibility: The image storage device may be a standard videotape recorder or any other video storage device. The storage device operates independently of the system controller.
The main advantage of this invention is the use of a master controller device, i.e., a microcontroller-based device able to perform several management functions. The master control unit does not depend on the video recording system. Thus, either the system or the master controller may be upgraded without major changes to the other part.
The slave system uses standard video cameras 68 (FIG. 7). The control signals reside in a separate bus (video bus 49 and control bus 51), so that the main system may detect video bus failures. In addition, the encoding of control signals is easier and independent of the video signal.